A good answer might be:

The instance variables are used to store the state of an object. They will hold values for as long as the object exists.

Parameters are Seen by their Own Method, Only

The formal parameters of a method can be "seen" only by the statements of their own method. This means that if a method tries to use a parameter of some other method, the compiler will find a syntax error.

Here is the CheckingAccount class again, this time with a new definition of the display() method

class CheckingAccount
{
  . . . .
  private int    balance;

  . . . .
  void  processDeposit( int amount )
  {
    balance = balance + amount ; 
  }

  // modified display method
  void display()
  {
    System.out.println( balance + "\t" + amount );
  }

}

QUESTION 4:

Is this display() method correct?